Fluxes of nitrous oxide and methane, and nitrogen leaching from organically and conventionally cultivated sandy soil in western Finland

Organic farming is considered to be environmentally beneficial partly due to the ban on synthetic fertilisers and pesticides, but there are few studies including direct measurements on the environmental impact of organic farming compared with the conventional system. In this study, greenhouse gas emissions and nitrogen leaching were compared in three different farming systems in western Finland. Two of them consisted of grass production and livestock raising, and were managed either organically (OF) or conventionally (CF). The third farming system was conventionally managed cereal production without livestock (CEF). Greenhouse gas (CH4 and N2O) fluxes, nitrogen leaching and soil mineral nitrogen concentrations were measured for 1 year from three replicate plots of each farming system. The annual flux of nitrous oxide (N2O) was 1.4 kg N ha−1 in OF, 1.2 kg N ha−1 in CF, and 3.5 kg N ha−1 in CEF. Annual methane (CH4) oxidation ranged between −0.72 and −0.44 kg CH4 ha−1 in the three treatments. In the case of OF and CF nitrogen losses to water were larger than gaseous losses as N2O but in CEF they were equal. Of the N added as mineral fertiliser and cattle slurry to the CF fields, 1.6% was lost by leaching, while 0.7% was lost to the atmosphere as N2O. In CEF, the respective percentages were 3.0% for N leaching and 3.2% for N lost to the air. The environmental advantages of organic compared with conventional farming systems were not confirmed in this study.